It has now released video footage which it believes shows the missing bird, and it suggests the tag must be faulty. The estate has also asked its lawyer to consider what possible action it might take.

The case is strikingly similar to an incident in County Durham last April in which Highlander, the hen harrier, was said to have disappeared and the finger was pointed at grouse shooters. It then reappeared this February, ten months later, suggesting that its tracking device had simply stopped working.

The Scottish estate said: “It's a shocker, the implication is pretty clear.

There's no doubt the transmitter has stopped working. They (the RSPB) say the suggestion is that the bird died and from what they have released they believe that the estate is implicated.

"The other implication is that they (eagles) are not welcome on the estate which they clearly are.”

The head ‘keeper filmed and photographed eagles on two separate occasions on Saturday and last Thursday and has sent the footage to the police.

Laura Sorrentino, director of the estate, said: “The RSPB allegations have been reckless and defamatory and the matter is now in the hands of our lawyers. The RSPB seems to accuse first and think later without caring about the damage it does.

“Because of the light and distance between the bird and the keeper we cannot be as certain that the Saturday afternoon footage is the same eagle but the head keeper is more confident that the later photographs could be the 338-tagged bird. We have submitted both to police and what this does show that eagles not only exist on our estate but are welcome.”

She added that the estate could have helped the RSPB with its investigation but claimed that when it visited the estate with police on Wednesday “its representatives were hooded and kept their faces covered”.

“We are a small estate surrounded by other sporting estates,” said Ms Sorrentino. “We firmly believe the issue of satellite tags needs very close examination as there is evidence of them developing faults.”

View photos

Conservationists accuse some grouse estates of persecuting raptors

Ian Thomson, RSPB Scotland head of investigations, said the police agreed that the circumstances were suspicious, claimed the tags were “very reliable” and said the fact that transmissions had stopped strongly suggested “the bird has died”.

A spokesman for the charity told the Daily Telegraph: "We don't know what's happened to the bird. The eagle has vanished without a trace. We would expect it to keep transmitting for a number of years.

"If they (the estate) have given the footage to the police then we would welcome that. We would expect many golden eagles to be out and about. It's not uncommon to see a number of eagles in the area.

"There have been a catalogue of eagles that have disappeared, all we can do is present the fresh information and let people draw their own conclusions.”